Summary
Stiction in control valve plays a negative role in the whole control system, thus, research on motion of stem is necessary to fix the stiction problem. Lots of researches focus more on the friction and spring force in the motion model of stem, neglecting the fluid force. However, fluid force is crucial in extremely high-pressure conditions. In this paper, the fluid force in the motion model of stem has been considered by using the Fluent UDF (User-Defined Function) method. And the response time of stem during the closing process has been calculated under step-function signal of p from actuator. By analyzing the fluid flow and stem’s motion, a turning point is observed which divides the closing process into two parts according to the feature of fluid force. Before it, the fluid force can be regarded as a constant, and after it, the fluid force is functioned as a nonlinear term. Based on this, a modified model is proposed, characterized as a piecewise function, adaptable to varying conditions.
